add: discord link

Author: shibe97

README.md

@@ -2,6 +2,8 @@
 
 It helps you to use microCMS from JavaScript and Node.js applications.
 
+<a href="https://discord.com/invite/K3DPqw4EJ2" target="_blank"><img src="https://img.shields.io/badge/Discord-%235865F2.svg?style=for-the-badge&logo=discord&logoColor=white" alt="Discord"></a>
+
 ## Getting Started
 
 ### Install